Cement composition and method of preparation



26 1 J July 927 A. M. NICOLSON CEMENT COMPOSITION AND METHOD OF PREPARATION Filed Sept 50. 192,

M van for; re /Wander M. Nico/son.

Patented July 26, 1927.

UNITED STATES PATENT OFFICE.

ALEXANDER M. NICOLSON, OF NEW YORK, N. Y.,

ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF YORK, N. Y., A CORPORATION OF NEW YORK.

CEMENT COMPOSITION AND METHOD OF PREPARATION.

Application filed September 30, 1924. Serial No. 740,746.

This invention relates to a composition of matter and particularly to a cement compo-' sition and to a method of making the same.

An object of the invention is to produce a good adhering cement having the characteristics of an insulator.

Another object of the invention is the production of a cement composition which is particularly Well adapted for use in. connection with piezo-electric crystal structure of Rochelle salt.

Still another object of the invention is a method of and means for preventing the desiccation of Rochelle salt compositions.

The single figure of the drawing illustrates some of the uses of this cement in connection with a loud speaking telephone receiver. There is represented a piezo-electric crystal 9 of the type described in my article on The Piezo-Electric Effect in the Composite Rochelle Salt Crystal, proceedings of the A. I. E. E., November, 1919, a e 1315. 'A crystal of this nature and its method of production are disclosed in my prior Patent 1,438,965, dated December 19, 1922,

Patent 1,590,311, dated June 29, 1926, and

Patent 1,562,578, dated November 24, 1925, and in my copending patent application Serial No. 621,704,. filed- February 28, 1923. The crystal 9 is here shown connected to the diaphragm 16 of a loud speaker. Such a crystal has the property of transforming an alternating current voltage communicated to it through the oppositely char ed girdle and pyramidal or internal electr es 14 and 13 respectively, into mechanical vibrations which may be, in turn, communicated to a tone plate 15 which actuates the diaphragm 16. It has been found desirable to join the various metallic and crystalline elements with a cement composition which will cut off electrical conductivity between the internal electrode 13 and the girdle electrode 14 and further, compound structure strong.

which will produce a which is mechanically In accordance with the features of this in ends of the pyramidal electrode at 17 and 18, to cement the lead 20 at the point 19 where it enters the pyramidal electrode, to cement the crystal to the base at 10, and to cement the metallic tone plate 15 to the top of the crystal. In these applications of this cement composition, advantage is taken of itsespeeially strong adhering properties and of its electrical insulating properties.

Where the wire '23 passes through the surface of the crystal, it may have a rubber or other electrically insulating covering as indicated at 24; a tube 25 of quartz or the like having high surface leakage resistance may also surround this portion of the wire 23. The cement composition of the present in vention is carefully placed around the elements 23, 24 and 25 where they pass through the crystal surface as indicated at 26.-

In the operation of the structure of the drawing, an alternating current voltage is applied between the leads 20 and 22-and is transmitted through the electrodes 13 and 14 to the crystal 9, whichtransforms this voltage into mechanical vibrations, which are in turn communicated to the tone plate 15, which actuates the diaphragm 16 of a loud speaker and, therefore, causes the production of sound waves in the air. I

In accordance with the features of this invention, there is provided a group of compositions comprising sodium potassium tartrate containin varying percentages of its water of crysta lization. It has been found that compositions composed of fused, and subsequently super-cooled, sodium potassium tartrate, NaKCJLO AH O, possess the adhering and insulating properties necessary in a cement for use in conjunction with R0- chelle salt piezo-electric appliances, for ex ample, and when properly proportioned will not be substantially amorphous and will not set too rapidly for practical use. The strength, insulating properties and time of setting of this group of compositions make them applicable over a wide range of conditions.

The proportions of water of crystallization retained by the crystalline mass after ther been noted that the composition becomes somewhat amorphous and loses considerable of its adhering properties with less water of crystallization retained.

In one method of pre aration, sodium potassium tartrate, Na C,H O,,.4H,O, is heated at a temperature between 74 C. (the nelting point of the crystallized salt) and l 0., and is then super-cooled. The time of heating or fusing will, of course, vary with the amount of sodium potassium tartrate used and with the amount of water of ample, that 5 cgstallization which it is desired to drive 0 Such a composition when prepared in the above manner is adapted for use, after being su er-cooled and before being allowed to solidi y.

The super-cooled composition may, however, be allowed to solidify and later, at some desired time, re-melted, without allowing appreciable further evaporation, and then super-cooled, when it is again adapted for application as'cement.

For ordinary applications as a cement it is usually desirable to drive off in the fusion process approximately 20% of the water of :rystallization. With small amounts of sodium potassium tartrate, 100 ams for example, the time required for t e fusion step has been found to vary from one to four minutes, dependin upon the temperature em loyed; specifica y, it has been noted that suc a sample will require about two minutes heating at C. for the production of a good cement composition.

The time required for cement compositions, as prepared b this method, to set has been found to vary rom five minutes to four hours, depending upon the amount of water which has been retained and upon the mass of cement used. It has been found, for exgrams of a composition containing approximately 80% of its water of crystallization will require only a few minutes to set, if agitated.

It is generally advisable to use sodium potassium tartrate which contains .all of its water of crystallization, so that standardized conditions for heating and setting may be determined. In case, therefore, partially dehydrated crystals are employed, it has been found desirable to add suflicient water before fusing to bring the total water content up to the water of c stallization value.

The preferred con itions of heating, that is, temperature and time, will depend to a great extent, upon the use to WhlCh the particular cement is to be ap lied. It is, of course, always desirable to rive ofi' sufficient water to roduce a strong adhering composition and it will depend u on the restrictions placed upon the time 0 setting asto the amount of water driven OE and, therefore, as to the time and temperature of fusion. It will be appreciated, therefore,

that it is not intended to impose any restrictions upon the proportions of water retained in the cement composition employed and therefore upon the conditions of heating, other than those set forth in the claims.

The cement composition of this invention is particularly well adapted for use in connection with Rochelle salt piezo-electric crystals, as the molecular compositions of both the cement and the surface to be cemented are the same, which, therefore, insures adherence. Further, the cement is of especial advantage in that it may be used at the point 21 of the drawing, bein" a plied as a star-shaped mass upon the insi e of the conical diaphragm 16 near its apex; such a mas of cement has been found to stiffen the diaphragm and to impart to it a high mechanical impedance corresponding to the impedance arc-w by the crystal.

It has been noted that the cement composition as produced above, when exposed to ordinary atmospheric conditions, shows a tendency toward a partial desiccation and, therefore, toward a decrease in its crystalline and adhesive values. It has been found that this desiccation may be reduced if the cement is maintained in an atmosphere humid at all times at a vapor pressure at least equal to that of the original hydrated sodium potassium tartrate crystals. Another feature of this invention resides, therefore, in the provision of a simple and effective preventative of the harmful drying action described above b maintaining an atmosphere humid at e vapor pressure of the original hydrated sodium potassium tartrate crystals.

One way of maintaining the condition of an atmosphere containing water vapor at a pressure at least equal to that of hydrated sodium potassium tartrate c stals around the cement, might be to varnis the exposed surfaces of the cement. Such a method has been described in my prior Patent 1,414,370, dated May 2, 1922, in connection with R0- chelle salt piezo-electric appliances; trouble has been encountered in this method, however, in the provision of a suitable varnish coating whic would be moisture-proof.

In accordance with this invention, the cement structure is enclosed with a quantity of efllorescent crystals such as hydrated sodium potassium tartrate, for example, within a metallic casin whose elements are substantially tight-fittin so as to allow only a limited circulation 0 air. Such a mass of eflioresoent c stals has been found to maintain the con ition of an atmosphere containing at all times an amount of water vapor which will exert a pressure at least equal to that of semi-hydrated sodium potassium tartrate. Sodium otassium tartrate is particularly well-a apted for use with the cement composition of this invens ll tion as the cement will lose appreciable water only after the mass of loose crystals has lost considerable of its water, at which time they may be replaced by fresh crystals. The mass of efilorescent crystals may be renewed from time to time as they-lose their water of crystallization.

This feature may also be emlployed to retard the desiccation'of Roche salt piezoelectric crystals by enclosing the c 1 within a similar casing to ther wit a quantity of efllorescent crysta i in connection with Rochelle salt crystals, it

is evident that the cement composition of this invention may be employed in any instance where a strong adhering or' insulating cement may be required, such as, for example, joining glass to glass, metal to metal, or glass to metal, and in other .situations; and.

further that this new use of efllorcsoent sub- .stances may be employed in any case where it is desirable to maintain an atmosphere containing water vapor at a pressure above some given ressure.

What is c aimed is: 1. A cement composition comprising fused and super-cooled sodium potassium tartrate crystals. V

2. The process of preparing a cement composition which comprises heating sodium potassium tartrate crystals to atleast its fusion tem rature and then super-cooling said heate mass.

3. The method of preparing a cement composition which comprises heating sodium potassium tartrate to at-least its melting point, super-cooling said mass, and a1 lowing said mass to solidify.

4. The method of preparing a cement composition which comprises heating amixture' of water and sodium tassium tartrate, and super-cooling sai heated mixture.

5; The process of preparing a cement composition which comprises heating sodium potassium tartrate crystals toa temperature 'atleast as other surface portion, an

said mass.

6. A method of prepar' a cement composition which comprises eating sodium potassium tartrate' to a temperature between 74 and 120 (3., and then super-cooling the heated mass.

-7. The process of preparingacement composition which comprises heating sodium potassium tartrate to at least its fusing temperature fora riod of time at-least suflicient to drive 0 approximately 20% of its total weight of water crystallization and super-cooling said heated mass. A

8. The process of preparing a cement comhigh as"74 C., and super-cooling f position which comprises heating sodium potassium tartrate to a temperature in the neighborhood of and at least as hi h as its fusing temperature for a period 0 time of from 1 to 4 minutes and supercooling said mass.

9. The combination with a; crystalline Rochelle salt body of Rochelle salt cement.

applied thereto.

10. A Rochelle salt crystal having two portions of its surface oppositely -electrified when said crystal is stressed, one of said portions being substantiall bounded by said a coating of cement substantially covering said one surface portion said cement comprising Rochelle salt with part of its water of crystallization removed. a

11'. A piezo electric crystal com rising poles of opposite signs, one of said po es ter minating in one en of said crystal and said other pole encircling said'one pole, .and a coating of Rochelle salt cement on said end of said crystal and substantially covering said termination of said one pole.

12. A Rochelle salt bod and a cement thereon comprising Roche 0 salt with part ALEXANDER MQ NIC'OLSON. 

